feat(infra): add OTel auto-instrumentations across all services

NestJS 6 services use getNodeAutoInstrumentations().

Python 2 services use FastAPIInstrumentor. Go 2 services use otelgin.

services/ai/src/ai/main.py

@@ -9,6 +9,7 @@ from fastapi import APIRouter, FastAPI
 from fastapi.responses import StreamingResponse
 from opentelemetry import trace
 from opentelemetry.exporter.otlp.proto.http.trace_exporter import OTLPSpanExporter
+from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
 from opentelemetry.sdk.trace import TracerProvider
 from opentelemetry.sdk.trace.export import BatchSpanProcessor
 from prometheus_client import make_asgi_app
@@ -61,6 +62,9 @@ app = FastAPI(
     lifespan=lifespan,
 )
 
+# OpenTelemetry FastAPI 自动埋点（HTTP 请求/响应 span）
+FastAPIInstrumentor.instrument_app(app)
+
 app.mount("/metrics", make_asgi_app())
 
 # 业务路由加 /ai 前缀，Gateway 代理 /api/v1/ai/* → /ai/*